Viliuisk encephalomyelitis is a progressive neurodegenerative disorder that is spreading from its traditional endemic loci in the Viliui Valley of Eastern Siberia to adjacent densely populated regions through affected migrants. In FY98, clinical and pathological features of this emerging contagious disease have been characterized. The advanced VE syndrome consists of progressive dementia and movement abnormalities, bradykinesia, impoverished movements and generalized stiffness, progressive spasticity and slow slurred speech. Inflammatory changes in the CSF were seen in more than 80% of patients throughout the illness. A slow virus etiology was suggested, but the causative agent has not been identified. Micronecrotic foci surrounded by inflammatory cells and organized into granulomas were the most characteristic features of acute and subacute VE. In patients with longer duration of illness (over 6 years), severe brain atrophy, neuron loss and gliosis were observed. In general, VE neuropathology suggests a chronic infection with an extensive inflammatory reaction.